Technical Overview and Abstract

This technical disclosure presents a highly efficient extrusion melting method specifically designed for low-melting-point polyester (LMPET). Furthermore, it details a specialized manufacturing process for producing high-quality LMPET composite fibers. In a significant departure from traditional techniques, this process directly feeds polyester wet chips into a hopper. Consequently, the conventional and energy-intensive requirements for crystallization and pre-drying are completely eliminated.

To achieve this, a sophisticated vacuum system is integrated to evacuate the hopper. Subsequently, the chips enter a precision screw extruder, where they are heated and melted. During this critical phase, the vacuum system actively removes moisture and volatile impurities from the molten polymer. In the next stage of production, the LMPET and conventional polyester (PET) melts are extruded separately through dedicated lines. They eventually enter a composite spinning assembly via equal-length distribution pipes to ensure uniform pressure.

Under precise metering and high-pressure conditions, these two distinct components mix within the assembly in a controlled ratio. Specifically, the inner core phase, consisting of conventional PET, is uniformly encapsulated by the skin phase of LMPET. Finally, the material is extruded from a spinneret to form high-performance composite fibers. Overall, this invention represents a significant improvement over traditional spinning processes by utilizing a vacuum-equipped extruder to streamline production.

Brief Description of Drawings

The following section provides a detailed technical description, accompanied by relevant drawings and embodiments. To illustrate the process clearly, Figure 1 shows the integrated extrusion-melting method and the subsequent manufacturing stages for the composite fibers.

technical description

technical description

List of Symbols in Figures:

  1. Hopper: The primary entry point for wet LMPET chips.

  2. Hopper vacuum suction device: Specifically used to evacuate air and initial moisture from the entry stage.

  3. Screw vacuum suction device: Designed to extract deep-seated moisture and impurities during the melting phase.

  4. LMPET screw extruder: The core equipment for processing low-melting-point polymers.

  5. Booster pump: Required to increase melt pressure before filtration.

  6. Filter: Ensures the removal of any particulate matter to protect the spinneret.

  7. LMPET melt distribution pipe: A specialized conduit for transporting the low-melt component.

  8. Box body: The temperature-controlled housing for the spinning components.

  9. Conventional polyester screw extruder: Processes standard PET for the fiber core.

  10. Conventional polyester melt distribution pipe: Ensures the PET melt reaches the assembly at the correct pressure.

  11. LMPET metering pump: Provides precise volume control for the sheath component.

  12. Conventional polyester metering pump: Provides precise volume control for the core component.

  13. Assembly: The final mixing and extrusion unit for the composite fiber.

I. Regarding Chemical Fiber Polyester Processing

1.1 Background Introduction and Industrial Context

In the modern textile industry, low-melting-point polyester fiber serves as a primary raw material. Specifically, it is essential for producing non-woven fabrics such as glueless cotton and spun cotton. Because of its unique properties, it offers excellent physical, mechanical, and environmental benefits. Currently, existing production technology relies heavily on direct spinning with LMPET melt. However, this direct spinning approach is often disadvantageous for manufacturers that need to change product types in response to shifting market demands.

Furthermore, traditional direct spinning requires a massive specific capacity to remain economically viable. As a result, it lacks the necessary flexibility to respond to volatile market conditions or small-batch orders. Historically, LMPET could not be effectively used for chip spinning. This was primarily because its crystallization speed is remarkably slow. Consequently, this slow speed made traditional drying to the required 30 ppm moisture level nearly impossible. Therefore, despite its limitations, direct spinning was previously the industry’s only adopted solution.

1.2 The Core Purpose of the Invention

The primary purpose of this invention is to provide a revolutionary extrusion melting method. Specifically, it aims to produce LMPET composite fibers while maintaining a very low viscosity drop. To illustrate its efficiency, the process ensures a viscosity drop of only 0.002–0.006 dl/g after the melting stage. By achieving this stability, the resulting fibers maintain superior structural integrity compared to those produced by traditional methods.

1.3 The Proposed Technical Solution

In response to the limitations mentioned above, the proposed method involves directly feeding vacuum-state LMPET wet chips into a screw extruder. Initially, this avoids the 40–50 hour crystallization delay seen in older models. Furthermore, a vacuum suction system is employed to remove moisture and impurities during the actual melting process.

To ensure quality, a high-precision thermometer monitors the extruded melt. This ensures the temperature remains strictly between 140–190°C. Subsequently, a booster pump pressurizes the melt to 80–140 kg/cm².

Detailed technical specifications include:

  • Heating Zones: The screw extruder features five distinct heating zones. These are carefully set between 140–190°C to facilitate a gradual and stable melt.

  • Vacuum Degrees: During vacuum extrusion, the suction system extracts harmful moisture. Specifically, the screw’s melting zone maintains a vacuum degree of 2–15 mbar. In contrast, the hopper vacuum degree is set between 0.5–5.0 mbar.

  • Material Properties: The LMPET chips utilized here have a melting point of 105–130°C. Notably, even after extrusion and vacuum suction, the viscosity decreases by only a negligible 0.002–0.006 dl/g.

II. Manufacturing Method Using a Vacuum Extruder

2.1 The Extrusion and Mixing Process

In this manufacturing stage, low-melting-point polyester and conventional polyester are extruded from their respective machines. Consequently, they remain isolated until they enter the composite spinning assembly. This transport occurs through equal-length distribution pipes to maintain synchronized flow rates.

Under precise metering and high pressure, the components mix in a specific, predetermined ratio. During this phase, the inner core phase (PET) is uniformly encapsulated by the skin phase (LMPET). Finally, the combined melt is extruded from the spinneret to form the final fiber.

2.2 Operational Parameters and Pressure Control

When the LMPET melt leaves the extruder, several critical steps occur. First, a booster pump pressurizes it to 80–140 kg/cm². Second, the melt passes through a filter to ensure purity. Third, it is distributed into six separate spinning assemblies via six equal-length pipes. This distribution is vital for maintaining product consistency across the entire production line.

Moreover, the LMPET and conventional PET melts are mixed in a specific ratio within these assemblies. To ensure accuracy, the LMPET metering pump operates with a supply capacity of 300–400 g/min. Furthermore, it maintains a rotational speed of 20–30 r/min.

In terms of thermal properties:

  • LMPET typically melts at a range of 105–130°C.

  • In contrast, conventional polyester melts at a much higher 256–261°C.

  • Consequently, the system must manage these different thermal profiles simultaneously.

  • Regarding scale, the extruder can handle capacities ranging from 35 kg/h to 1.5 T/h.

2.3 Distinct Advantages Over Traditional Processes

The most significant advantage of this process is that it feeds vacuum-state wet chips directly into the screw extruder. Therefore, by removing moisture and impurities via vacuum, it eliminates the need for bulky and slow crystallization dryers.

Additionally, the spinning process is continuous and highly automated. As a result, it features a much shorter equipment flow and a significantly smaller footprint in the factory. Specifically, this overcomes the major drawbacks of traditional processes. Those older methods required 40–50 hours of drying. Furthermore, they often suffered from unstable quality, which frequently disrupted normal spinning operations.

2.4 Conclusion and Industrial Value

In summary, this innovative method provides a streamlined path for the production of low-melting-point polyester composite fibers. By leveraging vacuum technology during the extrusion phase, manufacturers can achieve higher flexibility and lower energy costs. Moreover, the ability to bypass the crystallization stage allows for a faster response to market changes. Ultimately, this technology ensures that the resulting fibers meet the high standards required for modern non-woven and industrial applications, while also promoting a more efficient and stable manufacturing environment.

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